Heretofore, the methods of assembling and joining a decorative cover to the underlying padding material typically fell within one of the following techniques: mechanically retained assembly, adhesive bonded assembly and foamed-in-place (also known as molded-in-place) assembly. Such assemblies have found use as, for example, vehicle seats.
In the mechanically retained assembly, the seat cover is cut and sewn to shape, and thereafter joined to the padding material by means of metal "hog rings" or "C" clips which join molded in wires in the seat pad to sewn-in-wires in the trim cover. Alternatively, the securing means could be "hook and loop" devices (commercially available under the trade name Velcro) wherein the "hook" is molded into the seat pad and the "loop" is either sewn in or laminated onto the seat cover material. Unfortunately, this mechanically retained assembly is deficient. For example, the method of manufacturing this assembly is relatively complicated in that auxiliary wires or "hooks" must be molded into or glued on the seat pad. Further, auxiliary wire pockets or loop sheeting must be sewn in or laminated onto the seat cover material. Still further, the cost of these mechanical auxiliary means is onerous when compared to the cost of the foam padding material and the seat cover material. This results in a seat which is produced in a relatively complicated manner and at a relatively high expense.
In the adhesive bonded assembly, a molded foam seat pad or fabricated seat pad with the desired style and surface contours is located in a die or fixture. An adhesive in the form of a liquid, powder or film is applied to the surface of the pad. The seat cover material is held in a separate fixture and formed to the finished shape using one or more of vacuum (pressure), heat set and steam. The seat cover material with the die fixture is then registered to the pad. Thereafter, application of heat, steam and pressure activates the adhesive and joins the seat pad to the seat cover material. This assembly is deficient in that the method of manufacturing it requires the use of external heat, steam, vacuum and relatively high pressure. Further, this typically requires the use of a relatively expensive and toxic adhesive to bond the seat pad to the seat cover material.
In the foamed-in-place assembly, a mold is used comprising a lower section and an upper section. The seat cover material is located in the lower section of the mold and held in place with mechanical devices and/or with application of a vacuum. An impervious barrier is applied to the underside of the cover to prevent foam penetration into the cover and to permit the vacuum to form fit the cover. Thereafter, liquid polyurethane foam is poured onto the interior surface of the seat cover (i.e. onto the impervious barrier). The upper portion and lower portion of the mold are then closed thereby sealing the mold, and remain closed until the foam is set in the desired shape. During the process, the foam gives off expansion gases and expands substantially upwardly and away from the cover to fill the mold. In the finished item, the expanded foam adheres directly to the impervious barrier. This assembly is deficient in that it requires the use of external pressure and vacuum. The assembly also requires the use of an impervious backing to vacuum form the seat cover material to the lower section of the mold and to prevent bleeding of the liquid foam through the cover material. Since this method of assembly requires that no venting of expansion gases occur at the surface of the cover material, the use of the impervious backing is required with all cover materials, including vinyl and leather, which, when sewn together, become air permeable. Further, the use of the backing results in prevention of "breathing" of the finished system; this is undesirable since it reduces the comfort value of the finished system.
There have been attempts to produce covered seats wherein the impervious backing is omitted from the production process. Indeed, French patent 2,510,471 relates to the fabrication of padded elements suitable for use as seat bases or seatbacks, especially for vehicles. The manufacturing process described in the patent comprises placing the outer lining in the bottom of a mold, setting against the lining a pre-formed foam block having formed therein at least one cell or intermediate chamber, introducing a foamable mixture into the intermediate chamber to form a foam filling mass adhering to the facing portion of the lining, and removing the product from the mold. According to a preferred embodiment illustrated in FIG. 6 of the French patent, the foamable material is introduced into the intermediate chamber through a hole 14 in the upper outer shell of the foam block. The French patent purportedly does away with the need for the impervious backing utilized in the foamed-in-place assembly discussed above. However, the process disclosed in the French patent is deficient since it requires the use of a pre-formed cushion member having a substantial volume. Further, since the liquid foam is poured directly onto (i.e. no impervious backing), and thus expands in a direction substantially away from, the cover material, there is an increased likelihood that "foam densification" will occur. Foam densification is a phenomenon which occurs when young foam (i.e. foam which has just begun to expand from the liquid state) is forced to expand in an environment which is unable to accommodate the pressure build-up from gas given off from the expanding foam mass. This results in the expanding foam mass being "driven" into the cover material with a force which results in the occurrence of foam densification. When this occurs, the surface of the cover material, which, in many cases is intended to be the finished surface of the article, has a relatively hard surface which belies the objective of providing a resilient, finished article.
U.S. Pat. No. 4,618,532 discloses an upholstered seat having an air-permeable covering and a cold foam core. A process for producing the upholstered seat is also disclosed and comprises: providing a sealed split mold in which the dividing plane extends through the edge which is formed by the finished seat surface; placing a sealed air- and foam-impermeable covering material in the internal contour of the mold; clamping under tension that portion of the covering material which forms the actual seal surface in the dividing plane of the mold; placing a liquid foam in the sealed mold cavity; allowing the liquid foam to expand to fill the sealed mold cavity; and mechanically destroying the impermeable portion of the covering material. This reference concedes that adhesion between the foam and the covering material is not always achieved and thus, the use a covering material which has anchoring straps mounted on the interior surface thereof is necessary. Throughout the patent, it is disclosed that stitching seams for aesthetic purposes or for the anchoring straps must be sealed. The use of paper as an air- and foam-impermeable layer is recommended. The process disclosed by this reference is deficient since it requires the use of a sealed split mold and the use of an impermeable layer which must be mechanically destroyed after the process is completed. Further, the process is deficient since adhesion between the foam and the cover material is not consistently achieved. These deficiencies result in the requirement to use more complicated materials and extra process steps resulting in a process which is inefficient and relatively expensive to use.
In addition to the above-identified deficiencies of the prior art assemblies, extreme care must be taken with these assemblies when working with vinyl and with relatively exotic seat cover materials such as leather. For example, application of heat and steam to leather during the manufacturing of the assembly can permanently denature the leather thereby altering its texture and/or appearance. Further, the application of heat and steam can alter the gloss level of vinyl and also tends to wash out the grain surface.
It would be desirable to have a simple process for the manufacture of a padded element, which process could be used with virtually all conventional cover materials and which could be used to manufacture padded elements in a relatively efficient manner. It would be desirable if such a process could be utilized to adhere the entire finished surface of the trim cover to the cushion member.